linux.git/Documentation/networking/ip-sysctl.txt, branch v3.13

ipv4: improve documentation of ip_no_pmtu_disc

2013-12-17T20:20:15+00:00

Signed-off-by: Hannes Frederic Sowa 
Signed-off-by: David S. Miller

tcp: tsq: restore minimal amount of queueing

2013-11-14T21:25:14+00:00

After commit c9eeec26e32e ("tcp: TSQ can use a dynamic limit"), several
users reported throughput regressions, notably on mvneta and wifi
adapters.

802.11 AMPDU requires a fair amount of queueing to be effective.

This patch partially reverts the change done in tcp_write_xmit()
so that the minimal amount is sysctl_tcp_limit_output_bytes.

It also remove the use of this sysctl while building skb stored
in write queue, as TSO autosizing does the right thing anyway.

Users with well behaving NICS and correct qdisc (like sch_fq),
can then lower the default sysctl_tcp_limit_output_bytes value from
128KB to 8KB.

This new usage of sysctl_tcp_limit_output_bytes permits each driver
authors to check how their driver performs when/if the value is set
to a minimum of 4KB.

Normally, line rate for a single TCP flow should be possible,
but some drivers rely on timers to perform TX completion and
too long TX completion delays prevent reaching full throughput.

Fixes: c9eeec26e32e ("tcp: TSQ can use a dynamic limit")
Signed-off-by: Eric Dumazet 
Reported-by: Sujith Manoharan 
Reported-by: Arnaud Ebalard 
Tested-by: Sujith Manoharan 
Cc: Felix Fietkau 
Signed-off-by: David S. Miller

tcp: properly handle stretch acks in slow start

2013-11-05T00:57:59+00:00

Slow start now increases cwnd by 1 if an ACK acknowledges some packets,
regardless the number of packets. Consequently slow start performance
is highly dependent on the degree of the stretch ACKs caused by
receiver or network ACK compression mechanisms (e.g., delayed-ACK,
GRO, etc).  But slow start algorithm is to send twice the amount of
packets of packets left so it should process a stretch ACK of degree
N as if N ACKs of degree 1, then exits when cwnd exceeds ssthresh. A
follow up patch will use the remainder of the N (if greater than 1)
to adjust cwnd in the congestion avoidance phase.

In addition this patch retires the experimental limited slow start
(LSS) feature. LSS has multiple drawbacks but questionable benefit. The
fractional cwnd increase in LSS requires a loop in slow start even
though it's rarely used. Configuring such an increase step via a global
sysctl on different BDPS seems hard. Finally and most importantly the
slow start overshoot concern is now better covered by the Hybrid slow
start (hystart) enabled by default.

Signed-off-by: Yuchung Cheng 
Signed-off-by: Neal Cardwell 
Signed-off-by: Eric Dumazet 
Signed-off-by: David S. Miller

tcp: enable sockets to use MSG_FASTOPEN by default

2013-11-05T00:57:47+00:00

Applications have started to use Fast Open (e.g., Chrome browser has
such an optional flag) and the feature has gone through several
generations of kernels since 3.7 with many real network tests. It's
time to enable this flag by default for applications to test more
conveniently and extensively.

Signed-off-by: Yuchung Cheng 
Signed-off-by: Neal Cardwell 
Acked-by: Eric Dumazet 
Signed-off-by: David S. Miller

net: ipv6: mld: document force_mld_version in ip-sysctl.txt

2013-09-04T18:53:21+00:00

Document force_mld_version parameter in ip-sysctl.txt.

Signed-off-by: Daniel Borkmann 
Cc: Hannes Frederic Sowa 
Acked-by: Hannes Frederic Sowa 
Signed-off-by: David S. Miller

tcp: TSO packets automatic sizing

2013-08-29T19:50:06+00:00

After hearing many people over past years complaining against TSO being
bursty or even buggy, we are proud to present automatic sizing of TSO
packets.

One part of the problem is that tcp_tso_should_defer() uses an heuristic
relying on upcoming ACKS instead of a timer, but more generally, having
big TSO packets makes little sense for low rates, as it tends to create
micro bursts on the network, and general consensus is to reduce the
buffering amount.

This patch introduces a per socket sk_pacing_rate, that approximates
the current sending rate, and allows us to size the TSO packets so
that we try to send one packet every ms.

This field could be set by other transports.

Patch has no impact for high speed flows, where having large TSO packets
makes sense to reach line rate.

For other flows, this helps better packet scheduling and ACK clocking.

This patch increases performance of TCP flows in lossy environments.

A new sysctl (tcp_min_tso_segs) is added, to specify the
minimal size of a TSO packet (default being 2).

A follow-up patch will provide a new packet scheduler (FQ), using
sk_pacing_rate as an input to perform optional per flow pacing.

This explains why we chose to set sk_pacing_rate to twice the current
rate, allowing 'slow start' ramp up.

sk_pacing_rate = 2 * cwnd * mss / srtt

v2: Neal Cardwell reported a suspect deferring of last two segments on
initial write of 10 MSS, I had to change tcp_tso_should_defer() to take
into account tp->xmit_size_goal_segs

Signed-off-by: Eric Dumazet 
Cc: Neal Cardwell 
Cc: Yuchung Cheng 
Cc: Van Jacobson 
Cc: Tom Herbert 
Acked-by: Yuchung Cheng 
Acked-by: Neal Cardwell 
Signed-off-by: David S. Miller

ipv6: drop fragmented ndisc packets by default (RFC 6980)

2013-08-29T19:32:08+00:00

This patch implements RFC6980: Drop fragmented ndisc packets by
default. If a fragmented ndisc packet is received the user is informed
that it is possible to disable the check.

Cc: Fernando Gont 
Cc: YOSHIFUJI Hideaki 
Signed-off-by: Hannes Frederic Sowa 
Signed-off-by: David S. Miller

ipv6: make unsolicited report intervals configurable for mld

2013-08-14T00:05:04+00:00

Commit cab70040dfd95ee32144f02fade64f0cb94f31a0 ("net: igmp:
Reduce Unsolicited report interval to 1s when using IGMPv3") and
2690048c01f32bf45d1c1e1ab3079bc10ad2aea7 ("net: igmp: Allow user-space
configuration of igmp unsolicited report interval") by William Manley made
igmp unsolicited report intervals configurable per interface and corrected
the interval of unsolicited igmpv3 report messages resendings to 1s.

Same needs to be done for IPv6:

MLDv1 (RFC2710 7.10.): 10 seconds
MLDv2 (RFC3810 9.11.): 1 second

Both intervals are configurable via new procfs knobs
mldv1_unsolicited_report_interval and mldv2_unsolicited_report_interval.

(also added .force_mld_version to ipv6_devconf_dflt to bring structs in
line without semantic changes)

v2:
a) Joined documentation update for IPv4 and IPv6 MLD/IGMP
   unsolicited_report_interval procfs knobs.
b) incorporate stylistic feedback from William Manley

v3:
a) add new DEVCONF_* values to the end of the enum (thanks to David
   Miller)

Cc: Cong Wang 
Cc: William Manley 
Cc: Benjamin LaHaise 
Cc: YOSHIFUJI Hideaki 
Signed-off-by: Hannes Frederic Sowa 
Signed-off-by: David S. Miller

Revert "net: sctp: convert sctp_checksum_disable module param into sctp sysctl"

2013-08-09T20:09:41+00:00

This reverts commit cda5f98e36576596b9230483ec52bff3cc97eb21.

As per Vlad's request.

Signed-off-by: David S. Miller

net: sctp: convert sctp_checksum_disable module param into sctp sysctl

2013-08-09T18:33:02+00:00

Get rid of the last module parameter for SCTP and make this
configurable via sysctl for SCTP like all the rest of SCTP's
configuration knobs.

Signed-off-by: Daniel Borkmann 
Signed-off-by: David S. Miller